抗氧化系统在热激诱导的玉米幼苗耐热性形成中的作用

玉米幼苗经过42℃热激4h并恢复4h后,显著提高了玉米幼苗在高温处理下的存活率。热激并恢复4h后,不同程度地提高了抗氧化酶系统过氧化氢酶(CAT),超氧化物歧化酶(SOD),谷胱甘肽还原酶(GR),抗坏血酸过氧化物酶(APX)和过氧化物酶(GPX)的活性以及抗氧化剂还原型抗坏血酸(ASA)和谷胱甘肽(GSH)的含量,且经过热激的玉米幼苗在高温处理期间及其后的恢复过程中均能保持相对较高的抗氧化酶活性和抗氧化剂水平,说明保持较高的抗氧化酶活性和抗氧化剂水平是热激诱导的玉米幼苗耐热性形成的生理基础之一。     

热激锻炼对高温胁迫下菊花生理代谢的影响

以菊花(Chrysanthemum morifolium)品种'神马'的扦插苗为试验试材,在40℃下对其进行8 h的热激锻炼,然后在50℃下分别进行0、 1、 1.5、 2、 2.5、4 h不同时间的高温胁迫.通过对其相对电导率、丙二醛(MDA)、脯氨酸和可溶性蛋白质含量及过氧化物歧化酶(POD)和超氧化物歧化酶(SOD)活性的测定,研究了热激锻炼对菊花耐热性的影响.结果表明,热激锻炼的菊花叶片相对电导率比对照减小,MDA含量也比对照减小,而可溶性蛋白质和脯氨酸含量及POD和SOD活性比对照增加,说明热激锻炼在一定程度上提高了菊花幼苗的耐热性.     

水杨酸诱导的玉米幼苗适应高温和低温胁迫的能力与抗氧化酶系统的关系

玉米种子经水杨酸(SA)预处理后其幼苗的耐热性与耐冷性提高.其中以300μmol·L-1SA预处理的玉米幼苗对46℃高温胁迫2 d的耐热性提高最大,150μmol·L-1SA预处理的玉米幼苗对1℃低温胁迫5 d的耐冷性提高最大.在高温和低温胁迫过程中,SA预处理过的玉米幼苗中过氧化氢酶(CAT)、抗坏血酸过氧化物酶(APX)、过氧化物酶(GPX)、超氧化物歧化酶(SOD)和谷胱甘肽还原酶(GR)的活性水平均高于未经SA处理的.     

谷胱甘肽还原酶和超氧化物歧化酶在玉米幼苗热激诱导的交叉适应中的作用

玉米幼苗经过热激处理后,在随后的高温、低温、干旱和盐胁迫环境中,其存活率明显高于未热激的幼苗,表明热激能提高植物的抗热性、抗冷性、抗旱性和抗盐性,证实了玉米幼苗交叉适应现象的存在;热激还可提高谷胱甘肽还原酶(GR)和超氧化物歧化酶(SOD)的活性,且在上述4种胁迫过程中GR、SOD活性水平与玉米幼苗的存活率呈正相关,表明GR和SOD参与玉米幼苗交叉适应的形成.     

低温胁迫对苜蓿幼苗存活及生理生化指标的影响

用秋眠级为2级至9级的11个苜蓿品种,每品种被随机分为对照组和5个处理组,研究低温胁迫和苜蓿品种对幼苗存活和叶片生理生化指标的影响。结果表明:低温胁迫和苜蓿品种对幼苗存活率、叶片生理生化指标的影响均极显著,而且二者对它们的互作效应也极显著。子叶期幼苗在-7.5℃下处理12 h,存活率仅为3.26%。幼苗在-5℃下处理12 h,存活率为54.73%,但叶片游离脯氨酸含量、过氧化物酶活性、质膜相对透性和根系活力极显著提高;每天把幼苗置于-5℃下2 h至3 h锻炼7天,幼苗存活率可提高到95%以上,叶片游离脯氨酸、可溶性糖、可溶性蛋白质含量,超氧化物歧化酶活性、根系活力和质膜相对透性均极显著提高。结果表明:4级至9级品种的存活率极显著低于2级至3级的品种;6级至9级品种叶片游离脯氨酸含量、过氧化物酶活性、质膜相对透性极著显低于2级至3级的品种。     

热激对水稻幼苗耐冷性及热激蛋白合成的诱导

萌发的水稻种子经42℃热激处理后其幼苗的耐冷性明显增强,膜伤害程度降低,脯氨酸含量增加,超氧物歧化酶(SOD)、过氧化氢酶(CAT)、过氧化物酶(POD)活性和抗氧化物质抗坏血酸含量增加,而膜脂过氧化的关键酶脂氧合酶(LOX)活性及其产物丙二醛(MDA)含量下降.并且热激诱导萌发的水稻胚合成78、70、64、60、46、38、24、17、16kD的热激蛋白(HSP),其中属于HSP70的内质网结合蛋白(BiP)的合成与水稻幼苗耐寒性的提高有关.     

酿酒酵母耐热元器件的筛选

以提高酿酒酵母耐热性、降低乙醇发酵过程控温能耗成本为目的,通过分析嗜热栖热菌(Thermus thermophiles)HB8热激蛋白基因,设计并构建了5个热激蛋白元器件,并导入酿酒酵母。通过梯度升温培养筛选出性能较好的耐热元器件FBA1p-groes-SLM5t,并利用恒定高温培养进一步验证了含有该元器件的酿酒酵母工程菌S.c-Gro ES具有良好的耐热性,研究表明在42℃培养48h的存活率是对照的3倍。此外,FBA1p-groes-SLM5t还能提高酵母的抗氧化性,42℃下菌株S.c-Gro ES的ROS水平比对照低37.6%,H2O2处理1 h后存活率是对照的1.62倍,说明耐热元器件在缓解热胁迫的同时对细胞的抗氧化性也有帮助。耐热工程酿酒酵母S.c-Gro ES,其40℃发酵乙醇产量相对于30℃对照和40℃对照分别提高了25%和13.8%。嗜热菌热激蛋白的引入可以明显提高酿酒酵母的耐热性及其乙醇合成效率。     

抗氧化系统在H2O2诱导的玉米幼苗耐热性形成中的作用

H2O2预处理可显著增强玉米幼苗的耐热性.H2O2预处理后,玉米幼苗抗氧化酶谷胱甘肽还原酶(GR)、超氧化物歧化酶(SOD)、过氧化氢酶(CAT)和抗坏血酸过氧化物酶(APX)的活性及还原型抗氧化剂抗坏血酸(ASA)和谷胱甘肽(GSH)的水平显著提高,且H2O2预处理过的幼苗在高温处理期间及其后的恢复过程中均能保持相对较高的抗氧化酶活力和还原型/氧化型抗氧化剂比例.     

钙-钙调素与小麦苗中热激蛋白的诱导

在 34℃热激条件下 ,种子经钙预处理的小麦苗中的钙调素含量随着热激时间的延长而增加 ,热激 90min时达最大值 ,而种子用钙离子螯合剂EGTA预处理的小麦苗中钙调素含量无明显增加。种子用EGTA及钙调素拮抗剂CPZ和TFP预处理的小麦幼苗在 34℃热激时 ,热激蛋白的合成量减少。 4d的小麦幼苗在34℃或 37℃热激条件下 ,能诱导耐热性的获得 ,分别用EGTA、钙离子通道阻断剂易博定、钙调素拮抗剂TFP或CPZ预处理种子后 ,所得幼苗热诱导的耐热性的提高程度有所下降     

外源一氧化氮提高一年生黑麦草抗冷性机制

用不同浓度的一氧化氮(NO)供体硝普纳(sodiumnitroprusside,SNP)处理低温胁迫下1年生黑麦草幼苗,探讨外源NO对提高黑麦草幼苗抗冷性的作用。结果表明外源NO能减缓低温胁迫下黑麦草幼苗质膜相对透性的增加,促进脯氨酸(Pro)的积累,提高超氧化物歧化酶(SOD)、过氧化氢酶(CAT)和过氧化物酶(POD)保护酶活性,其中POD酶活性的提高尤为显著。恢复生长时,经SNP处理的幼苗膜透性、脯氨酸和保护酶活性恢复较快,其中0.5mmol/LSNP处理的效果最为明显,0.2、1.0mmol/LSNP处理的效果次之。     

Hydrogen sulfide donor sodium hydrosulfide-improved heat tolerance in maize and involvement of proline

Hydrogen sulfide (H₂S) has long been considered as a phytotoxin, but nowadays as a cell signal molecule involved in growth, development, and the acquisition of stress tolerance in higher plants. In the present study, hydrogen sulfide donor, sodium hydrosulfide (NaHS), pretreatment markedly improved germination percentage of seeds and survival percentage of seedlings of maize under heat stress, and alleviated an increase in electrolyte leakage of roots, a decrease in tissue vitality and an accumulation of malondialdehyde (MDA) in coleoptiles of maize seedlings. In addition, pretreatment of NaHS could improve the activity of Δ¹-pyrroline-5-carboxylate synthetase (P5CS) and lower proline dehydrogenase (ProDH) activity, which in turn induced accumulation of endogenous proline in maize seedlings. Also, application of proline could enhance endogenous proline content, followed by mitigated accumulation of MDA and increased survival percentage of maize seedlings under heat stress. These results suggest that sodium hydrosulfide pretreatment could improve heat tolerance of maize and the acquisition of this heat tolerance may be involved in proline.     

Effect of pretreatment with hydrogen sulfide donor sodium hydrosulfide on heat tolerance in relation to antioxidant system in maize (Zea mays) seedlings

Hydrogen sulfide (H₂S) is a signal molecule that is involved in plant growth, development and the acquisition of stress tolerance including heat tolerance, but the mechanism of H₂S-induced heat tolerance is not completely clear. In present study, the effect of sodium hydrosulfide (NaHS), a H₂S donor, treatment on heat tolerance of maize seedlings in relation to antioxidant system was investigated. The results showed that NaHS treatment improved survival percentage of maize seedlings under heat stress in a concentration-dependent manner, indicating that H₂S treatment could improve heat tolerance of maize seedlings. To further study mechanism of NaHS-induced heat tolerance, catalase (CAT), guaiacol peroxidase (GPX), superoxide dismutase (SOD), glutathione reductase (GR) and ascorbate peroxidase (APX) activities, and glutathione (GSH) and ascorbic acid (AsA) contents in maize seedlings were determined. The results showed that NaHS treatment increased the activities of CAT, GPX, SOD and GR, and GSH and AsA contents as well as the ratio of reduced antioxidants to total antioxidants [AsA/(AsA+DHA) and GSH/(GSH +GSSG)] in maize seedlings under normal culture conditions compared with the control. Under heat stress, antioxidant enzymes activities, antioxidants contents and the ratio of the reduced antioxidants to total antioxidants in control and treated seedlings all decreased, but NaHS-treated seedlings maintained higher antioxidant enzymes activities and antioxidants levels as well as the ratio of reduced antioxidants to total antioxidants. All of above-mentioned results suggested that NaHS treatment could improve heat tolerance of maize seedlings, and the acquisition of this heat tolerance may be relation to enhanced antioxidant system activity.     

Hydrogen sulphide may be a novel downstream signal molecule in nitric oxide‐induced heat tolerance of maize (Zea mays L.) seedlings

Nitric oxide (NO) is a second messenger with multifunction that is involved in plant growth, development and the acquisition of stress tolerance. In recent years, hydrogen sulphide (H₂S) has been found to have similar functions, but crosstalk between NO and H₂S in the acquisition of heat tolerance is not clear. In this study, pretreatment with the NO donor sodium nitroprusside (SNP) improved the survival percentage of maize seedlings and alleviated an increase in electrolyte leakage and a decrease in tissue vitality as well as accumulation of malondialdehyde, indicating that pretreatment with SNP improved the heat tolerance of maize seedlings. In addition, pretreatment with SNP enhanced the activity of L‐cystine desulfhydrase, which, in turn, induced accumulation of endogenous H₂S, while application of H₂S donors, NaHS and GYY4137, increased endogenous H₂S content, followed by mitigating increase in electrolyte leakage and enhanced survival percentage of seedlings under heat stress. Interestingly, SNP‐induced heat tolerance was enhanced by application of NaHS and GYY4137, but was eliminated by inhibitors of H₂S synthesis DL‐propargylglycine, aminooxyacetic acid, potassium pyruvate and hydroxylamine, and the H₂S scavenger hypotaurine. All of the above‐mentioned results suggest that SNP pretreatment could improve heat tolerance, and H₂S may be a downstream signal molecule in NO‐induced heat tolerance of maize seedlings.     

Heat shock-induced ascorbic acid accumulation in leaves increases cadmium tolerance of rice (Oryza sativa L.) seedlings

Ascorbic acid (AsA) is the most abundant antioxidant in plants and plays a role in responding to oxidative stress. It has been shown that AsA plays a role in protecting against abiotic stresses. Rice seedlings stressed with 5 μM CdCl₂ showed typical Cd toxicity (chlorosis and increase in malondialdehyde content). Rice seedlings pretreated with heat shock at 45°C (HS) or H₂O₂ under non-HS conditions resulted in the increase in ascorbic acid (AsA) content and the AsA/dehydroascorbate ratio in rice leaves. Exogenous application of AsA or L-galactonone-1, 4-lactone (GalL), a biosynthetic precursor of AsA, under non-HS conditions, which resulted in an increase in AsA content in leaves, enhanced subsequent Cd tolerance of rice seedlings. Pretreatment with imidazole, an inhibitor of NADPH oxidase, under HS conditions significantly decreased H₂O₂ and AsA contents in leaves and reduced subsequent Cd tolerance of rice seedlings. We also observed that pretreatment with lycorine, which is known to inhibit the conversion of GalL to AsA, significantly inhibited HS-induced AsA accumulation in leaves and reduced HS-induced protection against subsequent Cd stress of rice stress. It appears that HS- or H₂O₂-induced protection against subsequent Cd stress of rice seedlings is mediated through AsA. The time-course analyses of HS in rice seedlings demonstrated that the accumulation of H₂O₂ preceded the increase in AsA. Based on the data obtained in this study, it could be concluded that the early accumulation of H₂O₂ during HS signals the increase in AsA content, which in turn protects rice seedlings from oxidative damage caused by Cd.     

The effect of heat shock on paclitaxel production in Taxus yunnanensis cell suspension cultures: role of abscisic acid pretreatment

The heat shock (HS) response is a conserved cellular defense mechanism to elevated temperatures, observed in cells from bacteria to human. It is characterized by the increased accumulation of HS proteins. This work examines the effect of HS on the secondary metabolite biosynthesis of cultured plant cells. Suspension cultures of Taxus yunnanensis cells, which produce the anticancer diterpenoid paclitaxel (Taxol), were heat shocked at 35-50 degrees C for 30-60 min. The results show that HS reduced cell viability and growth but significantly induced paclitaxel production. The HS-induced paclitaxel production depended on the intensity of HS and the physiological state of the cells. Abscisic acid (ABA)-pretreatment not only increased cell viability and growth upon HS but also improved HS-induced paclitaxel yield. The best culture phase to apply the HS was the late-exponential growth phase. Under the optimized condition, HS enhanced paclitaxel yield by sixfold to 6.8 mg/L. In addition, a prior mild-HS treatment also significantly increased HS-induced paclitaxel production. Furthermore, HS induced oxidative burst, the early event of plant defense response to pathogen attack and other stress challenge; the addition of putative inhibitors of lipoxygenase, a key enzyme for jasmonic acid biosynthesis, significantly inhibited HS-induced pacliatxel accumulation. The stimulation of secondary metabolite production by HS may be a result of HS-induced plant cell defense response.     

Proline accumulation is inhibitory to Arabidopsis seedlings during heat stress

The effect of proline (Pro) accumulation on heat sensitivity was investigated using transgenic Arabidopsis (Arabidopsis thaliana) plants ectopically expressing the Δ(1)-pyrroline-5-carboxylate synthetase 1 gene (AtP5CS1) under the control of a heat shock protein 17.6II gene promoter. During heat stress, the heat-inducible expression of the AtP5CS1 transgene was capable of enhancing Pro biosynthesis. Twelve-day-old seedlings were first treated with heat at 37 °C for 24 h to induce Pro and then were stressed at 50 °C for 4 h. After recovery at 22 °C for 96 h, the growth of Pro-overproducing plants was significantly more inhibited than that of control plants that do not accumulate Pro, manifested by lower survival rate, higher ion leakage, higher reactive oxygen species (ROS) and malondialdehyde levels, and increased activity of the Pro/P5C cycle. The activities of antioxidant enzymes superoxide dismutase, guaiacol peroxidase, and catalase, but not those of glutathione reductase and ascorbate peroxidase, increased in all lines after heat treatment, but the increase was more significant in Pro-overproducing seedlings. Staining with MitoSox-Red, reported for being able to specifically detect superoxide formed in mitochondria, showed that Pro accumulation during heat stress resulted in elevated levels of ROS in mitochondria. Interestingly, exogenous abscisic acid (ABA) and ethylene were found to partially rescue the heat-sensitive phenotype of Pro-overproducing seedlings. Measurement of ethylene and ABA levels further confirmed that these two hormones are negatively affected in Pro-overproducing seedlings during heat stress. Our results indicated that Pro accumulation under heat stress decreases the thermotolerance, probably by increased ROS production via the Pro/P5C cycle and inhibition of ABA and ethylene biosynthesis.     

Synergistic effect of antioxidant system and osmolyte in hydrogen sulfide and salicylic acid crosstalk-induced heat tolerance in maize (Zea mays L.) seedlings

Salicylic acid (SA), is a plant hormone with multifunction that is involved in plant growth, development and the acquisition of stress tolerance. Hydrogen sulfide (H₂S) is emerging similar functions, but crosstalk between SA and H₂S in the acquisition of heat tolerance is not clear. Our recent study firstly reported that SA treatment enhanced the activity of L-cysteine desulfhydrase (L-DES), a key enzyme in H₂S biosynthesis, followed by induced endogenous H₂S accumulation, which in turn improved the heat tolerance of maize seedlings.¹ In addition, NaHS, a H₂S donor, enhanced SA-induced heat tolerance, while its biosynthesis inhibitor DL-propargylglycine (PAG) and scavenger hydroxylamine (HT) weakened SA-induced heat tolerance. Also, NaHS had no significant effect on SA accumulation and its biosynthesis enzymes phenylalanine ammonia lyase (PAL) and benzoic-acid-2-hydroxylase (BA2H) activities, as well as significant difference was not observed in NaHS-induced heat tolerance of maize seedlings by SA biosynthesis inhibitors paclobutrazol (PAC) and 2-aminoindan-2-phosph- onic acid (AIP) treatment.¹ Further study displayed that SA induced osmolytes (proline, betaine and trehalose) accumulation and enhancement in activity of antioxidant system in maize seedlings. These results showed that antioxidant system and osmolyte play a synergistic role in SA and H₂S crosstalk-induced heat tolerance of maize seedlings.     

Participation of H2O2 in Enhancement of Cold Chilling by Salicylic Acid in Banana Seedlings

The possible physiological mechanism of enhancement of cold tolerance by salicylic acid (SA) in banana seedlings (Musa acuminata cv. Williams 8188) was explored. Measurements of leakage electrolyte after 2 d of recovery at 30/22 ℃ (day/night) following 3 d of cold stress at 7 ℃ showed that pretreatment with hydroponic solution containing SA 0.3－0.9 mmol/L as foliar spray under normal growth conditions (30/22 ℃) could significantly enhance cold tolerance of banana plants. The highest enhancing effect of SA occurred at 0.5 mmol/L and it showed the lowest leakage rate of electrolyte or smaller leaf wilting area after 2 d of recovery at normal temperature from 3 d of 7 ℃ or 5 ℃ cold stress. Higher concentrations (≥2.5 mmol/L) of SA, however, caused more electrolyte leakage, indicating that they aggravated chilling damage. Enhanced cold tolerance by SA could be related to H2O2 metabolism. Compared with water-treated seedlings (control), SA 0.5 mmol/L treatment inhibited activities of catalase (CAT) and ascorbate peroxidase (APX), increased peroxidase (POX) activity, but did not affect the activity of superoxide dismutase (SOD) under normal growth conditions, and these changes might lead to an accumulation of H2O2, whereas SA pretreatment enhanced the activities of CAT and APX, and reduced the increase in productions of H2O2 and thiobarbituric acid-reaction substances (TBARS) during subsequent 7 ℃ cold stress and recovery periods. Exogenous H2O2 treatments (1.5－2.5 mmol/L) also increased cold tolerance of banana seedlings. Furthermore, pretreatment of banana seedlings with dimethylthiourea (a trap for H2O2) significantly inhibited cold tolerance induced by SA. These results suggested that endogenous H2O2 may be required for SA-enhanced cold tolerance. The significance of the interaction of SA, H2O2 and H2O2-metabolizing enzymes during cold stress has been discussed.